The present invention relates to an electromagnetic wave detecting device which is capable of detecting electromagnetic waves including radiation (such as X-rays), visible light, and infrared light.
Conventionally, in the field of medical diagnosis, an image pickup device adopting an S/F (Screen/Film) mode, a CR (Computed Radiography) mode or an I.I-TV (Image Intensifier TV) mode has been used as a means to photograph an X-ray image. Note that, the S/F mode utilizes intensifying screens and films. The CR mode reads a latent image recorded on an imaging plate with laser scanning. The I.I-TV mode utilizes an electron multiplier tube and a CCD in combination. In addition, as a new type of the image pickup device replacing all of them, a flat panel two-dimensional image detecting device has been developed more actively in recent years.
The new two-dimensional image detecting device is made up of a combination of an active-matrix array which is used as a key device having a switching element disposed in a two-dimensional state and a converting element (detecting element) which converts electromagnetic wave information to an electric charge.
This two-dimensional image detecting device falls roughly into an xe2x80x9cindirect converting systemxe2x80x9d and a xe2x80x9cdirect converting systemxe2x80x9d depending on a difference of the principles of detecting the electromagnetic wave. The xe2x80x9cindirect converting systemxe2x80x9d first converts electromagnetic wave information, such as X-rays, to light through Scintillator, thereafter converting the light to an electric signal through a photodiode. On the other hand, the xe2x80x9cdirect converting systemxe2x80x9d converts the electromagnetic wave information, such as X-rays, directly to the electric signal through a semiconductor film. Note that, as the latter, the xe2x80x9cdirect converting systemxe2x80x9d, specific structures and principles of the device are described in, for example, {circle around (1)} US patent gazette U.S. Pat. No. 5,132,541 (Date of Patent: Jul. 21, 1992), {circle around (2)} D. L. Lee, et al., xe2x80x9cA New Digital Detector for Projection Radiographyxe2x80x9d, SPIE, 2432, pp.237-249, 1995, and the like.
Here, the principles of an electromagnetic wave detecting device (two-dimensional image detecting device) 100 which is described in the above-mentioned document {circle around (2)} is shown in FIG. 8.
The electromagnetic wave detecting device 100 has a single common bias electrode 102 and a plurality of charge collector electrodes 103 which are respectively formed on upper and lower layers of a semiconductor film 101 made of Se showing electromagnetic wave conductivity. Further, the charge collector electrodes 103 are respectively connected to charge storage capacitance (hereinafter referred to as xe2x80x9cCsxe2x80x9d) 104 and a switching element (TFT) 105. Note that, a dielectric substance layer 106 which is a charge rejection layer is provided between the semiconductor film 101 and the bias electrode 102. Further, an electron rejection layer 107 which is a charge rejection layer is provided between the semiconductor film 101 and the charge collector electrodes 103. In addition, an external high-voltage power source 109 for applying bias voltage to the bias electrode 102 is provided.
When an electromagnetic wave, such as an X-ray, is incident onto the electromagnetic wave detecting device 100 thus arranged, a charge (an electron-positive hole pair) is generated inside of the semiconductor film 101. At this stage, the semiconductor film 101 and the Cs 104 are serially connected electrically. Therefore, by previously applying a bias voltage to the bias electrode 102, an electron of the charge (electron-positive hole pair) generated in the semiconductor film 101 moves to a positive (+) electrode side, and a positive hole of the charge (electron-positive hole pair) moves to a negative (xe2x88x92) electrode side, thereby storing the charge in the Cs 104. Furthermore, by turning on the switching element 105, the charge stored in the Cs 104 can be taken outside. By thus disposing the charge collector electrode 103, the Cs 104 and the switching element 105 in a two-dimensional state, and reading out charges in a line-sequential manner, it becomes possible to obtain two-dimensional information of an electromagnetic wave which is a detection target.
Further, generally, Se, CdTe, CdZnTe, PbI2, HgI2, SiGe, Si, etc. are used as a semiconductor film which has electromagnetic wave conductivity. Among these, an Se film shows desirable electromagnetic wave conductivity with respect to X-ray application. Also, the Se film is capable of large-area deposition at a low temperature by vacuum evaporation. For those reasons, the Se film is widely used for the electromagnetic wave detecting device having a structure (the structure disclosed in the foregoing documents {circle around (1)} and {circle around (2)}) in which a semiconductor film is formed directly on an active matrix substrate.
Further, CdTe and CdZnTe are the materials that show desirable electromagnetic wave conductivity with respect to X-ray application. However, since CdTe and CdZnTe need to be deposited at a high deposition temperature, it is not possible to form them direct on the active matrix substrate. Therefore, a semiconductor film of CdTe or the like is formed on a different supporting substrate first, thereafter joining the active matrix substrate to the substrate having the semiconductor film, thereby making up an electromagnetic wave detecting device of a hybrid structure. The electromagnetic wave detecting device of the hybrid structure thus using the CdTe or CdZnTe film is described in document {circle around (3)} Y. Izumi, et al., xe2x80x9cA Direct Conversion X-ray Sensor with A Novel Hybrid Panel Structurexe2x80x9d, AM-LCD99 DIGEST OF TECHNICAL PAPERS, pp. 49-52, 1999.
Incidentally, the switching element array 105 (active matrix substrate) used for the electromagnetic wave detecting device as discussed is formed under normal circumstances by having a glass substrate as a base, on which a metal film (Al, Ta, etc.), a semiconductor film (a-Si, p-Si, etc.) and an insulating film (SiNx, SiOx, etc.) are deposited. Further, it is possible to form components, such as electrical wiring, a TFT element and the like, by patterning switching element arrays 105 in a predetermined form.
However, as the electromagnetic wave detecting device discussed above, in the case that an inorganic material such as Se or the like is deposited on the active matrix substrate having the glass substrate 108 as its base, a problem described below occurs.
The thermal expansion coefficient of a glass substrate is 3-8(xc3x9710xe2x88x926/xc2x0 C.), and the thermal expansion coefficient of an Se film is 30-50(xc3x9710xe2x88x926/xc2x0 C.). Namely, as the glass substrate and the Se film have about 10 times difference in their thermal expansion coefficients, the semiconductor film peels off the glass substrate when an environmental temperature varies to the extent of xc2x120xc2x0 C. to xc2x130xc2x0 C. Especially, as shown in FIG. 8 of a prior art example, in the case of an arrangement such that a semiconductor film (Se) covers substantially the whole surface of the active matrix substrate as a continuous film, the influence of the difference between the two thermal expansion coefficients is likely to be pronounced as the size of the substrate becomes larger, that is, the removal of the semiconductor film is likely to occur in the vicinity of the substrate. Therefore, an electromagnetic wave detecting device using the Se film as a semiconductor film can be used in an environment under the limited, small range of temperature. Accordingly, an environment under a constant temperature should be maintained in the case of using or carrying the electromagnetic wave detecting device using the Se film, thereby arising such a problem as to cause extra works and costs.
Besides, the glass substrate has high solidity and poor flexibility. This flattens a detecting surface of the electromagnetic wave detecting device, thereby distorting a detection image when detecting an electromagnetic wave which spreads radially. In order to suppress the distortion, for example, Japanese Unexamined Patent Publication No.56255/2000 (Tokukai 2000-56255 published on Feb. 25, 2000) discloses a technique of disposing flat sensors on a curved plane. However, in this case, the presence of a space between the sensors prevents acquisition of continuous data. Besides, a slight distortion occurs, as each detecting device is flat.
Furthermore, in the case of the so-called xe2x80x9chybrid structurexe2x80x9d electromagnetic wave detecting device which has the active matrix substrate having the glass substrate as its base and a different substrate which has the semiconductor film formed thereon, which are connected with each other, there arises a problem described below.
In the case where a film surface of the semiconductor film has poor flatness, or the semiconductor film has a warp, a space between two substrates partially becomes wide when joining the supporting substrate to the active matrix substrate, and a poor connection is likely to occur. Especially when depositing an inorganic material, such as CdTe or the like, a high temperature process of about 500xc2x0 C. is necessary. Therefore, even a slight difference between the thermal expansion coefficient of the supporting substrate and that of the film made of an inorganic material such as CdTe or the like greatly warps the supporting substrate. Note that, a thickness of the semiconductor film is about 300 xcexcm, and a thickness of a conductive connecting material is 8 xcexcm-10 xcexcm. Consequently, only when there tentatively emerges xc2x15% order of warpage, a poor connection occurs, thereby disabling image detection in a portion subject to the poor connection.
Further, no matter what structure of the electromagnetic wave detecting device or type of semiconductor film there may be used, a problem described below occurs wherever the active matrix substrate having the glass substrate as its base is used.
Commonly, a glass substrate has a large specific gravity. This raises a problem such that an electromagnetic wave detecting device using that substrate becomes heavy and poor in mobility. For example, in the case of examining a detection target by shifting the electromagnetic wave detecting device up-and-down and side-to-side, when components include the glass substrate, there arise a problem such that the weight of the glass substrate causes poor mobility, thereby preventing high speed movement. Moreover, the glass substrate is vulnerable to impact from the outside and easy to break. Therefore, the electromagnetic wave detecting device which has the glass substrate as its component needs a special impact absorbing mechanism. Besides, due to the property of the glass substrate as described, the electromagnetic wave detecting device having the glass substrate as its component should be covered with a protection material when carried. This raises problems that are production of extra works and costs, and inferior portability. In order to allow an ambulance to have an X-ray imaging device aboard in the future so as to enable use for an emergency treatment at an accident site and doctor""s use when visiting patients in their homes, etc., the electromagnetic wave detecting device should be improved in terms of its mobility and portability. The drawbacks of the glass substrate as discussed become especially pronounced when the electromagnetic wave detecting device is given a large screen.
It is a first object of the present invention to provide an electromagnetic wave detecting device which is lightweight, and has superior mobility and portability.
It is a second object of the present invention to provide a manufacturing method of an electromagnetic wave detecting device which is capable of obtaining image data which is free from poor connection and distortion.
In order to attain the first object, an electromagnetic wave detecting device according to the present invention includes:
a semiconductor film which generates a charge upon induction by an electromagnetic wave;
an active matrix array for reading out the charge which is generated in the semiconductor film,
wherein:
the active matrix array is formed by having a resin substrate as its base and detects the electromagnetic wave by a direct converting system.
With the foregoing arrangement, by using the active matrix array having the resin substrate as its base, the electromagnetic wave detecting device has superior impact-resistance, thereby allowing an active matrix substrate to be difficult to break. Therefore, since coverage by a protection material when carrying is not required, thereby omitting extra works and costs, and improving portability. Further, since resin has a smaller specific gravity than that of glass, the weight is greatly reduced, thereby improving mobility. Moreover, it is possible to simplify a special absorbing mechanism against impact from the outside, thereby suppressing manufacturing costs. Accordingly, it is possible to provide the electromagnetic wave detecting device which is lightweight and has superior mobility and portability. Note that, this effect becomes particularly effective when the electromagnetic wave detecting device has a large screen.
In order to attain the second object, a manufacturing method of an electromagnetic wave detecting device includes the steps of:
forming an active matrix array on one side of a resin substrate;
setting the resin substrate having the active matrix array formed thereon to a supporting material while deforming the resin substrate to a curved shape; and
depositing a semiconductor film on a surface of the active matrix array deformed to the curved shape.
With the foregoing procedure, the resin substrate is curved first, thereafter depositing a semiconductor film on the curved resin substrate, thereby making it possible to form the semiconductor film into the curved shape without causing a crack and/or exfoliation in the semiconductor film. Accordingly, even when the resin substrate and the semiconductor film have different thermal expansion coefficients, neither a space nor poor connection occurs between the resin substrate and the semiconductor film. As a result, image data can be detected continuously, thereby obtaining an image without distortion. Further, forming the semiconductor film in a state that the resin substrate is set on a supporting material suppresses deformation of the resin substrate during formation of the semiconductor film.
Additional objects, features, and strengths of the present invention will be made clear by the description below. Further, the advantages of the present invention will be evident from the following explanation in reference to the drawings.